The properties of surface Dirac fermions on a three-dimensional topological insulator in proximity to amagnetic insulator with spatially textured magnetization are considered. We present an exact analytical treatment of the domain-wall resistance and the spectrum for an extended generic domain wall with in-plane and out-of-plane magnetizations. In the latter case, we find oscillations in the domain-wall resistance as a function of the wall width and for certain widths a complete absence of reflections for all incoming momenta. The surprising occurrence of oscillations and the reflectionless potentials can be related to a supersymmetry of the surface Dirac Hamiltonian combined with the domain-wall profile.